A known challenge in the hydrogen generation art is to control the reaction rate between a chemical metal hydride, such as sodium borohydride, and a liquid, such as water or methanol. When the reaction is too slow, the fuel cell does not have sufficient hydrogen to generate electricity. When the reaction is too fast, the excess hydrogen gas can pressurize the fuel supply or hydrogen generator.
Heretofore, control of the reaction rate to produce hydrogen in a chemical metal hydride reaction has been accomplished by introducing the catalyst into a reaction chamber containing aqueous metal hydride and water to start the reaction and removing the catalyst from the aqueous metal hydride to stop the reaction, as disclosed in U.S. Pat. Nos. 6,939,329 and 3,459,510 and in U.S. Published Patent Application No. US 2005/0158595. This technique regulates the rate of reaction by controlling how much the catalyst interacts with the aqueous fuels or the duration of contact between the catalyst and the fuels.
Another method of controlling the reaction rate is to add metal hydride granules having uniform size into water at a steady rate to control the production of hydrogen, as discussed in U.S. Patent Publication No. US 2004/0184987. Another method is to control the injection rate of water and aqueous metal hydride solution to control their reaction rate.
However, there remains a need for methods and devices that can effectively control the reaction rate between the chemical metal hydride and the liquid reactant.